1. Field of the Invention
This invention relates to instruments for the noninvasive quantitative measurement of constituents in blood, such as blood glucose levels. Specifically, this invention relates to an improved analysis instrument utilizing a removable insert which facilitates positioning of an individual user's finger and improves the internal cleanliness of the instrument.
2. Description of the Background Art
Information concerning the chemical composition of blood is widely used to assess the health characteristics of both people and animals. For example, analysis of the glucose content of blood provides an indication of the current status of metabolism. Blood analysis, by the detection of above or below normal levels of various substances, also provides a direct indication of the presence of certain types of diseases and dysfunctions.
A current type of blood glucose analytical instrumentation is available for the specific purpose of determining blood glucose levels in people with diabetes. This technology uses a small blood sample from a finger poke which is placed on a chemically treated carrier and is inserted into a portable battery operated instrument. The instrument analyzes the blood sample and provides a blood glucose level reading in a short period of time.
A different class of blood glucose analytical instruments is the near-infrared quantitative analysis instrument which noninvasively measures blood glucose, such as the type described in U.S. Pat. No. 5,077,476 (Rosenthal). The noninvasive blood glucose measurement instrument analyzes near-infrared energy following interactance with venous or arterial blood, or transmission through a blood-containing body part. The instrument measures a change in light absorption that occurs, in part, due to the glucose content of the blood stream.
Non-invasive measurement instruments of this type have broad applications for the diabetic community. For example, people with diabetes have wide changes in their blood glucose content during the day which often require multiple measurements per day for good disease control. The ability to make these near-infrared blood glucose level measurements noninvasively means that more measurements will likely be made per day than would be made using the more painful blood drawing approach.
An example of a non-invasive measurement instrument is disclosed in the '476 patent wherein an individual user places the most distal portion of his or her finger within a "jaws" type arrangement. Light is then impinged upon the surface of the finger and a detector is placed axial with the light beam on the opposite side of the finger to receive any light emerging therefrom. A microprocessor receives the signal from the detector and calculates the user's blood glucose level.
Another analysis instrument is disclosed in copending application Ser. No. 07/565,302 which comprises a chamber formed in the instrument housing into which a user inserts his or her finger. The user's finger must be correctly placed within the chamber so that proper exposure to the near-infrared energy and detection can occur. In addition, this type of analysis instrument may measure the individual's skin temperature and use this measurement in calculating the blood analyte concentration. As a result, the individual's finger must properly be in contact with a skin temperature sensor to acquire the temperature measurement.
A possible limitation of the above-described instruments is that the instruments, optical systems can be damaged by the measurement of a person, especially children, having extremely dirty or wet fingers. Moreover, moisture and foreign matter can degrade optical transmission of the near-infrared energy thereby resulting in inaccurate blood glucose level measurements.
Another potential limitation associated with these instruments involves obtaining inaccurate blood glucose measurements resulting from a failure to properly and securely position a user's finger, which may vary widely in size, inside the instrument. This limitation is particularly applicable to taking measurements on a child's finger. Also, proper connection with a skin temperature sensor may not occur if an individual's finger is improperly positioned within the instrument's chamber.
Thus, there is a great need for an improved near-infrared analysis instrument having means for insuring the internal cleanliness of the instrument and means for more securely positioning an individual user's finger, which vary widely in size, inside the analytical instrument.